CIE Nov 2015 v3 Paper 3 Q2

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PMT FA 4 is an impure sample of hydrated calcium chloride, CaCl 2.2H2O. On heating, hydrated calcium chloride loses its water of crystallisation. CaCl 2.2H2O(s)CaCl 2(s) + 2H2O(g) You will determine the purity of FA 4 by measuring the loss in mass that occurs when it is heated. The impurity present in FA 4 is not decomposed on heating. (a) Method You should read the instructions carefully before starting any practical work and draw a table for your results in the space below.Weigh a crucible and record its mass. Add between 1.80 g and 2.00 g of FA 4 into the crucible. Reweigh the crucible and its contents and record the mass. Place the crucible on the pipe-clay triangle and heat gently for 1 minute and then strongly for a further 2 minutes. Allow the crucible and its contents to cool. Reweigh the crucible and contents and record the mass. Heat the crucible strongly for a further 2 minutes. Allow it to cool. Reweigh the crucible and contents and record the mass. Repeat the heating, cooling and weighing until you are satisfied that all the water of crystallisation has been removed. Calculate and record the mass of FA 4 used and the total mass of water lost. While you are waiting for the crucible to cool, you may wish to start work on Question 3. II III IV VI [6]UCLES 2015 9701/33/O/N/15<br /> PMT (b) Calculations Show your working and appropriate signi cantgures in thenal answer to each stage of your calculations. (i) The percentage loss in mass on heating is de ned as the loss in mass on heating100. the original mass Calculate the percentage loss in mass of FA 4. (ii) Calculate the percentage loss in mass when pure hydrated calcium chloride, CaCl 2.2H2O, is heated. percentage loss in mass =% (iii) Use your results to (i) and (ii) to calculate the percentage purity of FA 4, impure CaCl 2.2H2O. percentage loss in mass =% percentage purity =% [3] (c) A student carried out this experiment using 2.60 g of FA 4. Suggest whether this experiment would give a more accurate result for the percentage purity of FA 4. Explain your answer.[1]UCLES 2015 9701/33/O/N/15 [Turn over<br /> PMT (d) In your calculations you assumed that the impurity in FA 4 does not decompose on heating. State how the percentage purity that you calculated in (b)(iii) would change if the impurity were to decompose on heating. Explain your answer.[1] [Total: 11]UCLES 2015 9701/33/O/N/15<br />

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